The present invention relates generally to the art of forming bells on plastic pipes, and more particularly, is directed to an apparatus suitable to form an internal groove simultaneously with the belling of the pipe.
It is the usual practice to extrude plastic pipes in elongate configuration of desired diameter and then to cut the extruded product into individual lengths of convenient size suitable for handling, shipping and installing, for example twenty foot lengths. As each length of pipe is cut, it is presently the practice to enlarge or "bell" one end sufficiently to join adjacent pipe sections by receiving an unenlarged end of another similar length of pipe. The inside diameter of the bell is formed sufficiently large to receive easily one end of the next adjacent section of pipe with sufficient clearance to allow the appliction of packing, sealing materials, gaskets or other materials designed to prevent leakage at the pipe joints when the pipe lengths are joined to form a pipe line. In many applications, the seal between adjacent lengths of pipe is provided by expanding an internal groove in the bell of suitable configuration and design to permit the pipe joint to be easily and rapidly made and to prevent leakage upon completion of the system.
While experience has proved that the use of a formed gasket seated within an annular recess or groove formed in the bell of a pipe is an efficient and suitable construction for sealing joints between adjacent plastic pipe lengths, prior workers have encountered difficulties in the efficient formation of such annular grooves. It is usual to employ a single mandrel both to form the shaped bell and at the same time, to simultaneously also form the expanded groove for receipt therein of the annular gasket. Prior workers in the art have developed mandrels with various types of expanding segments in an effort to provide a composite, practical device which can rapidly and precisely form the required bell and groove in a single operation in a rapid and cost effective manner. Such prior mandrels have included equipment which utilizes pluralities of segment groups which are movable radially inwardly and outwardly and which cooperate to perform the required function of forming an expanded internal groove in the bell of the pipe as the pipe bell is formed by the mandrel. However, such prior art devices have suffered from construction and operating difficulties. Many devices were designed with two sets of completely different segments which operated in different paths and at different speeds. Sometimes, it was difficult to maintain precise alignment of the two groups of segments in their groove forming positions which misalignment could result in irregularities produced in the formation of the groove. Any imperfections or irregularities in the formed annular groove could result in imprefectly made joints. Upon utilizing the pipe sections to form a pipe system, such imperfections could cause a leakage, loss of pressure or other deleterious effects. Additionally, the prior machines which have been developed, because of their complexity, resulted in apparatus that was extremely costly in construction and bulky in installation and in use.